Wildcards ( * ) can be used to select unknown XML elements.
The following XPath expression selects all the child elements of all the cd elements of the catalog element:

/catalog/cd/*

The following XPath expression selects all the price elements that are grandchild elements of the catalog element:

/catalog/*/price

The following XPath expression selects all price elements which have 2 ancestors:

/*/*/price

The following XPath expression selects all elements in the document:

//*

And then I gathered it was an XML class not paleontology.